/*
Copyright 2014 Pinterest.com
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 */
package com.pinterest.jbender.intervals;

import java.util.Random;

/**
 * Poisson distribution request interval generator.
 */
public class ExponentialIntervalGenerator implements IntervalGenerator {
  private final double nanosPerQuery;
  private final Random rand;

  public ExponentialIntervalGenerator(int queriesPerSecond) {
    nanosPerQuery = 1000000000.0 / queriesPerSecond;
    this.rand = new Random();
  }

  @Override
  public long nextInterval(long nanoTimeSinceStart) {
    return (long) (-Math.log(rand.nextDouble()) * this.nanosPerQuery);
  }
}
